1. Field of the Invention
The invention relates to railroads generally, and more particularly to a system and method for determining wheel size to compensate for wheel wear.
2. Discussion of the Background
Controlling the movement of trains in a modern environment is a complex process. Collisions with other trains must be avoided and regulations in areas such as grade crossings must be complied with. The pressure to increase the performance of rail systems, in terms of speed, reliability and safety, has led to many proposals to automate various aspects of train operation. For example, positive train control (PTC) and automatic train control (ATC) systems have been widely discussed in recent years.
Some automated systems rely on global positioning system (GPS) receivers for indications of train speed and position (as used herein, xe2x80x9cglobal positioning systemxe2x80x9d and xe2x80x9cGP Sxe2x80x9d refer to all varieties of global positioning system receivers, including, but not limited to, differential global positioning system receivers. Still other systems use inertial navigation systems (INSs) for determining speed and location. However, GPS receivers and INSs sometimes fail, and for that reason it is desirable to have a back-up system.
One method that can be used in case of a positioning system failure is to measure the rotation of motor, axle or wheel rotation to determine the speed at which a train is traveling and/or the distance which a train has traveled. Each time the wheel makes a compete revolution, the distance traveled by the wheel is equal to its circumference in the absence of any slippage. Thus, if the radius R of the wheel is known, the distance traveled for each revolution of the wheel is equal to 2xcfx80R. However, the radius of a wheel changes over time due to wheel wear. For example, a standard train wheel can decrease in size from 40 inches to 36 inches over its useful life. Therefore, the distance traveled in each wheel revolution can vary between 125.7xe2x80x3 and 113.1xe2x80x3, a difference of approximately 12.6xe2x80x3 or 10%. This error is significant.
What is needed is a method and system that compensates for wheel wear.
The present invention meets the aforementioned need to a great extent by providing a method and system for compensating for wheel wear in which wheel rotation information from a revolution counter or a tachometer and position and/or speed information from an independent positioning system such as GPS or INS are measured over a predetermined distance and used to determine the size of the train wheels. This process is performed periodically to compensate for wheel wear.
In one aspect of the invention, the system includes a map database and the position information from the independent positioning system is used to as an index to ensure that the rotation data used for the speed/position comparison between the position system and rotation data is collected in an area of straight and flat track so as to exclude errors in the rotation data caused by wheel slippage and turns.
In another aspect of the invention, the data used for the comparison between the speeds/distances indicated by the positioning system and by the rotation data is collected over a long distance to minimize known errors in the positioning system.